Turbomolecular pumps (TMPs; sometimes also referred to as turbopumps) are widely employed for generating an ultra-high vacuum in an evacuated chamber. Vacuum pumps generally include turbo molecular pumps, drag pumps, centrifugal pumps, diffusion pumps, cryopumps, titanium sputter pumps, getter pumps and the like. In general, turbomolecular pumps are employed to compress gases, such as hydrogen in the 10−8 Pa (10−10 Torr) range, to pressures for evacuation through roughing pumps (about 10 Pa). The principle underlying turbomolecular pumps is that in high vacuum, where the molecular mean free path of the remaining gas is large compared to the dimensions of the chamber, fast moving rotors impart a linear momentum to fluid particles that interact with the rotors. The relative velocity imparted to a fluid stream by the alternating rotating blades and stator blades draws the fluid from the vacuum chamber to be evacuated to the pump exhaust outlet. Each set of rotor blades and stator blades is able to support a pressure difference. For a series of blade sets, the compression ratio for zero flow is approximately the product of the compression ratios for each set. Conventional turbomolecular pumps achieve high ratios of compression by operating at a high rotational speed and by employing a large number of rotor/stator blade sets.
With a high rotational speed and greater number of rotor/stator blade sets come increased difficulties in manufacturing the pumps and in their maintenance and repair, which increases overall operational costs.
Turbomolecular pumps are available commercially for applications where pumping speeds of up to a few thousand liters per second (liter/sec) are required. Conventional turbomolecular pumps are ill-suited to achieving ultra high pumping speeds, however. Ultra high pumping speeds require very large diameter pumps. Large pump diameters are not compatible with reaching large compression ratios economically.
Turbopump bearings must support the rapidly spinning rotor in high vacuum. The output stages can require reasonably high torque and power when starting a turbo pump. These requirements are harder to meet in a large diameter turbo pump. However, the required pumping speed sets the diameter size of the rotor, and requires a large diameter pump where ultra high speeds are needed.
These partially conflicting demands limit the bearing design options and leads to short bearing service life or reliance on complex electronics, for example to stabilize a magnetic bearing.
Existing pumps use many bearing designs, including metallic and ceramic ball bearings, with oil or grease lubrication; active and passive magnetic bearings; and combinations thereof. Hence turbomolecular vacuum pumps are complex, and expensive.
Certain applications require extremely high pumping speeds at ultra low pressures. Examples include space simulation chambers, fusion reactors, particle accelerators and detectors, large processing chambers such as mirror coaters, and experimental chambers such as LIGO interferometer arms or Kaon decay pipes.
Turbomolecular pumps would be the pumps of choice for these applications. However, conventional turbomolecular pumps are designed for high compression rates and only moderate pumping velocities, because their designs become quite difficult when scaling up to ultra high pumping speeds. Disadvantages to using turbomolecular pumps in such situations include: acquisition cost, the need for bearing regeneration or replacement, maintenance costs such as bearing replacements, contamination of the process chamber.
Because of these disadvantages, diffusion pumps, cryopumps, titanium sputter pumps and getter pumps are generally employed instead.
Thus, there is presently a need for an ultra high pumping speed vacuum evacuation apparatus, system, and method capable of reaching ultra high vacuum. There is additionally a need that such a vacuum evacuation apparatus be low cost, require minimum repair, have very high reliability, and have a very long life.